The present invention relates to fluid regulators. Fluid regulators are common devices utilized to reduce upstream pressure of a fluid to a lower downstream pressure compatible with use requirements. For example, gas may be stored at high pressure but can be usefully consumed only at low pressure, and regulators provide the pressure reduction. Fluid regulators employ a controlled valve element that admits to flow from a high pressure side to a low pressure side of the regulator. In one type of regulator, the valve element is controlled by surface areas acted upon by upstream and downstream pressure. A spring is commonly used to augment downstream pressure. When the downstream pressure is below regulated value, the valve element moves away from a seat in response to upstream pressure to permit increased flow. When the downstream pressure is sufficiently high and reaches the regulated value, the valve element maintains a fixed displacement from the seat. When the downstream pressure is higher than the regulated value, the downstream pressure forces the valve element close to the seat, restricting fluid flow. This type of system utilizes pressure differentials between upstream and downstream to effect a regulated constant downstream pressure. It is unsatisfactory in systems that have variable upstream pressure, for the lack of constancy of upstream pressure produces a variable downstream pressure.
A different type of regulator, a balanced regulator, produces regulation by a pressure differential between delivery pressure and some opposing fixed force source such as atmospheric pressure and a spring. When delivery pressure drops below a desired point, atmospheric pressure and the spring will urge a valve element further open to admit to the flow of more fluid. When the delivery pressure is at the desired level, it overcomes the effect of the atmospheric pressure and the spring moves the valve element further closed. The previous known types of balanced regulators have employed a valve element that is somewhat position-sensitive to supply side pressure.
A problem associated with regulation is that the force of a spring used to control orifice opening varies depending on the amount that the spring is stressed. This is a straightforward consequence of the well known fact that the force exerted by a spring is equal to a constant multiplied by the spring's displacement. When a spring is used to urge the valve towards an open position, as the valve opens the spring force drops slightly, resulting in the valve not opening in proportion to flow demand. This produces a lower than desired regulated pressure, an effect known as pressure droop. It is desirable to avoid this type of aberration because it affects the accuracy of regulation.
In the environment in which this invention evolved, natural gas stored in tanks is used as a fuel source for vehicles. The tanks are charged to some pressure, say 2400 p.s.i., and the gas from the tanks used in the limit to exhaustion, corresponding, say, to a pressure of 50 p.s.i. The gas experiences two stages of regulation. The first stage steps the pressure down from supply side pressure to some predetermined value, say 50 p.s.i. The second stage of regulation steps the pressure down from this value to a pressure compatible with introduction into a fuel-air mixer, typically a pressure of a few inches of water. The system is charged with high pressure natural gas through a check valve that admits to flow through it in a charging direction only.
Different vehicles use compressed natural gas. It is not possible, then, to have a general purpose layout of the various lines and hardware necessary to effect a compressed natural gas fueling system. It is therefore highly desirable to have the individual hardware components as adaptable as possible to the constrictions of different use environments.
Another problem that develops with the transport of some fluids is freezing of constituents upon expansion from high pressure to low pressure. Hydrates in natural gas, for example, can freeze and cause problems such as flow restrictions or even flow termination.
It is also highly desirable to have a regulator that is easily serviced, for example, one that can have its seals readily renewed, and to avoid fluid impingement on control surfaces that degrades the surfaces.
In such systems as a fuel system for vehicles it is obviously very desirable to close down the delivery system when there is a clandestine loss of pressure in order to avoid discharging the natural gas from the tanks.